Java Date & Time API Explained

1. What is the Date & Time API?

The Java Date & Time API provides classes to work with dates, times, durations, and time zones.

• Before Java 8, developers used Date and Calendar, which were confusing and not thread-safe.
• With Java 8, the java.time package was introduced (inspired by Joda-Time library).
• It is immutable, thread-safe, and much more powerful.

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2. Why was it needed?

• Old APIs (Date, Calendar) were poorly designed.
• Months started at 0 (January = 0 🤯).
• Time zones were hard to handle.
• Methods weren’t intuitive.

The new API solved these problems with cleaner, more reliable classes.

🔹 3. Key Classes in the Java Date & Time API

1. LocalDate → Represents only a date (no time).

import java.time.LocalDate;
public class Example {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        System.out.println("Today's Date: " + today);
    }
}

2. LocalTime → Represents only time (no date).

import java.time.LocalTime;
LocalTime time = LocalTime.now();
System.out.println("Current Time: " + time);

3. LocalDateTime → Represents date and time together.

import java.time.LocalDateTime;
LocalDateTime now = LocalDateTime.now();
System.out.println("Date & Time: " + now);

4. ZonedDateTime → Represents date-time with time zone.

import java.time.ZonedDateTime;
ZonedDateTime zone = ZonedDateTime.now();
System.out.println("Zoned Date & Time: " + zone);

5. Period & Duration → Represent amounts of time.

import java.time.*;
LocalDate start = LocalDate.of(2020, 1, 1);
LocalDate end = LocalDate.now();
Period period = Period.between(start, end);
System.out.println("Years passed: " + period.getYears());

6. DateTimeFormatter → For formatting and parsing.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

LocalDateTime now = LocalDateTime.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm");
System.out.println("Formatted Date: " + now.format(formatter));

4. Advantages of the New API

• Immutable & Thread-Safe (unlike old Date class).
• Readable & Easy-to-Use Methods.
• Time Zone Support (UTC, offsets, zones).
• Clear distinction between date, time, and datetime.

5. Summary

The Java Date & Time API (java.time) is one of the best additions in Java 8. It replaced confusing old APIs with a modern, clean, and powerful approach.

With classes like LocalDate, LocalTime, LocalDateTime, and ZonedDateTime, working with time has never been easier. It’s a must-know for any Java developer building real-world applications.

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